A free neutron at rest, decays into three particles: a proton, an electron and an anti neutrino.
`._(0)^(1)nrarr._(1)^(1)P+._(-1)^(0)e+vecv`
The rest masses are: `m_(n)=939.5656 MeV//c^(2)`
`m_(p)=938.2723 MeV//C^(2) m_(e)=0.5109 MeV//c^(2)`
In a particular decay, the antineutrino was found to have a total energy (including rest mass energy) of 0.0004 MeV and the momentum of proton was found to be equal to the momentum of electron. Find the kinetic energy of the electron.

Answer

0.7820 MeV